For convenience in handling powdered sorbent materials methods such as encapsulation of the powders, or forming mixtures of the powders and plastic resins into flexible sheets, or adhering the powders to flexible supports are known.
Plastic resins including polyolefins, poly(methyl methacrylate), poly(vinyl alcohol), ABS resins, and the like, have been mixed with sorbent powders and formed into sheet. These products have little or no gas permeability, and their rate of sorption is poor because the surface of the sorbent is substantially coated with the plastic resin.
Constructions in which sorbent powders are adhered to fabric or cloth supports with adhesives also have drawbacks, in that they have low durability as the sorbent powders can be easily dislodged by mechanical action. If the sorbent powders are adhered with sufficient adhesive to provide good durability, the sorbent surface is substantially coated with adhesive and the rate of sorption is poor.
Filters and other porous media comprising composite layered constructions containing powdered sorbent materials designed to adsorb, absorb, detoxify, or react with harmful or noxious vapors are known in the art. Likewise, protective clothing for hazardous or toxic chemicals comprising composite layered constructions containing powdered sorbent materials are also known in the art.
Such products and articles are often porous, that is, they have continuous pores or passageways through them so that gases and vapors can easily enter or pass through them thus accessing the sorbent powders. These products and articles function very effectively in dry environments or under conditions in which they are not contacted by liquids. When contacted by water, organic solvents, or other organic liquids, the sorbent powders may be wet by the liquids and their ability to sorb gases and vapors greatly reduced. "Liquid barrier" layers designed to prevent passage of harmful liquids may be used, and are typically positioned so as to prevent direct contact of the liquid with the sorbent material. Some such "liquid barriers" are air-permeable fabrics which have been treated with repellent finishes. Such systems lack in that they will allow aerosols and particulates to pass through, and with minimum pressure, liquids will pass. Other air-impermeable "liquid barriers" provide adequate protection against liquids but are water-vapor-impermeable or have limited water-vapor-permeability. Clothing lacking water-vapor-permeability do not "breathe", i.e. allow passage of water vapor and thus, are uncomfortable to the wearer.